Comparative organization of the claustrum: what does structure tell us about function?

Abstract

The claustrum is a subcortical nucleus present in all placental mammals. Many anatomical studies have shown that its inputs are predominantly from the cerebral cortex and its outputs are back to the cortex. This connectivity thus suggests that the claustrum serves to amplify or facilitate information processing in the cerebral cortex. The size and the complexity of the cerebral cortex varies dramatically across species. Some species have lissencephalic brains, with few cortical areas, while others have a greatly expanded cortex and many cortical areas. This evolutionary diversity in the cerebral cortex raises several questions about the claustrum. Does its volume expand in coordination with the expansion of cortex and does it acquire new functions related to the new cortical functions? Here we survey the organization of the claustrum in animals with large brains, including great apes and cetaceans. Our data suggest that the claustrum is not always a continuous structure. In monkeys and gorillas there are a few isolated islands of cells near the main body of the nucleus. In cetaceans, however, there are many isolated cell islands. These data suggest constraints on the possible function of the claustrum. Some authors propose that the claustrum has a more global role in perception or consciousness that requires intraclaustral integration of information. These theories postulate mechanisms like gap junctions between claustral cells or a “syncytium” to mediate intraclaustral processing. The presence of discontinuities in the structure of the claustrum, present but minimal in some primates, but dramatically clear in cetaceans, argues against the proposed mechanisms of intraclaustral processing of information. The best interpretation of function, then, is that each functional subdivision of the claustrum simply contributes to the function of its cortical partner.

Parvalbumin expression in the claustrum of the adult dog. An immunohistochemical and topographical study with comparative notes on the structure of the nucleus

“…According to our findings we can hypothesize either that this structure is not part of the claustrum or that it is a part of the posterior claustrum. This latter hypothesis might be in line with the discontinuities described by Baizer et al (2014) in the claustrum of animals with large brains although in the histological sections we did not find a clear discontinuity between the claustrum and the cloud of neurons. However, following the former hypothesis, these neurons might represent the posterior extent of the insular pocket.…”

“…Moreover, in the light of recent anatomical studies (Baizer et al, 2014;Johnson et al, 2014) we analyzed the histological features of this enigmatic structure. Although many immunohistochemical studies have shown the presence of PV in the claustrum of different animals 1 Dachshund 11 Female 11 64 Intra-abdominal hemorrhage 2 Fox terrier 12 Male 10 66 Peritonitis 3 Mixed-breed 4 Male 14.5 70 Trauma 4 Mixed-breed 9 Male 16 72 Heart failure * Formalin fixed.…”

Psychedelics

“…Nevertheless, it is generally accepted today that the claustrum exhibits widely distributed reciprocal anatomic projections to virtually all regions of the cortex as well as to many subcortical structures, including the hippocampus, amygdala, and caudate nucleus. Substantial evidence now exists that the major target of claustral projections is the cortex, and that the major input to the claustrum comes from the cortex (see reviews by Smythies et al, 2012Smythies et al, , 2014Baizer et al, 2014;Mathur, 2014;Torgerson and Van Horn, 2014).…”

“…Although Crick and Koch (2005) proposed that the claustrum might mediate consciousness, or provide perceptual integration across sensory modalities, Baizer et al (2014) argue against this hypothesis, stating that intraclaustral processing would require that the claustrum be a continuous structure, which it is not in every species. Furthermore, as the cortex has expanded through evolution in different species, the size of the claustrum has actually decreased in relative size (Kowianski et al, 1999).…”

Subcortical connections of the perirhinal, postrhinal, and entorhinal cortices of the rat. II. efferents

“…This strong connectivity is unsurprising given the vast cortical connections of the claustrum itself. Because its function is still unknown, with suggestions ranging from the simple facilitation of cortical function (Baizer et al, 2014), to the basis of consciousness (Crick and Koch, 2005), it is difficult to speculate as to the role this anatomical connection might have.…”